Accuracy and reliability of noninvasive stroke volume monitoring via ECG-gated 3D electrical impedance tomography in healthy volunteers

Abstract

Cardiac output (CO) and stroke volume (SV) are parameters of key clinical interest. Many techniques exist to measure CO and SV, but are either invasive or insufficiently accurate in clinical settings. Electrical impedance tomography (EIT) has been suggested as a noninvasive measure of SV, but inconsistent results have been reported. Our goal is to determine the accuracy and reliability of EIT-based SV measurements, and whether advanced image reconstruction approaches can help to improve the estimates. Data were collected on ten healthy volunteers undergoing postural changes and exercise. To overcome the sensitivity to heart displacement and thorax morphology reported in previous work, we used a 3D EIT configuration with 2 planes of 16 electrodes and subject-specific reconstruction models. Various EIT-derived SV estimates were compared to reference measurements derived from the oxygen uptake. Results revealed a dramatic impact of posture on the EIT images. Therefore, the analysis was restricted to measurements in supine position under controlled conditions (low noise and stable heart and lung regions). In these measurements, amplitudes of impedance changes in the heart and lung regions could successfully be derived from EIT using ECG gating. However, despite a subject-specific calibration the heart-related estimates showed an error of 0.0 ± 15.2 mL for absolute SV estimation. For trending of relative SV changes, a concordance rate of 80.9% and an angular error of −1.0 ± 23.0˚were obtained. These performances are insufficient for most clinical uses. Similar conclusions were derived from lung-related estimates. Our findings indicate that the key difficulty in EITbased SV monitoring is that purely amplitude-based features are strongly influenced by other factors (such as posture, electrode contact impedance and lung or heart conductivity). All the data of the present study are made publicly available for further investigations.

Noninvasive measurement of stroke volume changes in critically ill patients by means of electrical impedance tomography

“…Finally, it has also been shown in healthy volunteers that EIT-based SV estimation is sensitive to perturbations from electrode-skin contact problems or changes in posture [29]. The latter has also been reported for cardiac EIT signals in general [30,38].…”

“…Without this exclusion a less good performance of CR = 85.0% and R = 0.54 (P < 0.001) was obtained (results not shown). This highlights the sensitivity of our approach to perturbations such as electrode-skin contact problems [29], EIT belt displacement [18] or large changes in ventilation [30]. Thus, contrary to the amplitude in the heart region, SV trending via the amplitude in the lung region might be more promising.…”

Unobtrusive Estimation of Cardiovascular Parameters with Limb Ballistocardiography

“…There are non-invasive options such as volume-clamping techniques [18,19] and applanation tonometry [20], but these techniques require costly equipment and/or trained operators. The gold standard stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR) likewise require inconvenient and costly procedures such as dye injection [21], echocardiography [22], impedance cardiography [23], and electrical impedance tomography [24]. The CV parameters have also been derived indirectly using the so-called pulse contour methods [25,26,27,28,29].…”

Comparison of bolus- and filtering-based EIT measures of lung perfusion in an animal model

“…Based on results showing a common relationship between the effect of gravity and perfusion in both children and adults (Bhuyan et al 1989), in newborns we expect to see a comparable directional change in perfusion due to the changes in posture. Recently, Braun et al (2018) evaluated EIT's ability to monitor cardiac output, showing that EIT is more reliable for monitoring cardiac output trends than absolute cardiac output. EIT has also been investigated for monitoring of systemic blood pressure (Solà et al 2011), and for monitoring of pulmonary arterial pressure (Proença et al 2017).…”